1. Field of the Invention
This invention relates to the recovery of petroleum from a subterranean reservoir by the injection of fatty alcohol followed by the injection of soap.
2. Description of the Prior Art
The crude oil which accumulates in subterranean reservoirs is normally produced initially by so-called "primary recovery" techniques which utilize only the natural forces present in the reservoir environment. However, upon depletion of these natural forces a major portion of the crude oil remains trapped within the reservoir rocks. Also some petroleum reservoirs cannot be produced by reliance on natural forces alone. Recognition of the large amount of crude oil remaining in such reservoirs has led to the development of a number of "enhanced recovery" techniques which are designed to economically recover additional quantities of this remaining oil.
The most common enhanced recovery technique is that of "waterflooding" in which an aqueous solution is injected into the reservoir under pressure sufficient to drive the solution through the reservoir and out through production wells so as to effect a displacement of the petroleum from the rock pores and a driving of this oil by the waterflood to the producing wells. Economics dictate that waterflooding can only be used advantageously when the cost of the equipment, water and any additional chemical additives is less that the value of the oil recovered by the process. Accordingly, the efficiency of the waterflood is critical to the success of the process.
Probably the single most important obstacle that an effective waterflood must overcome is the high interfacial tension between water and oil. This causes in part the capillary retention of the oil within the pores of the reservoir rock and prevents the displacement of the oil droplets by water under the pressures feasible in reservoir flooding processes. In consequence, various aqueous surfactant systems have been proposed for use in enhanced recovery waterflooding methods. Their object is to reduce the interfacial tension between oil and water from a characteristic value of about 35 dynes per centimeter to a value of something less than one dyne per centimeter. By employing techniques well known in the art, many of these surfactant flooding processes are not effective at common reservoir brine concentrations however. Such surfactant processes can be used both during initial waterflooding operations and after the reservoir has "watered-out".
Spontaneous emulsion flooding is a particular method of enhanced oil recovery that operates by creating an emulsion by the action of the aqueous flooding solution on the in place oil. The process simultaneously lowers the interfacial tension and creates an oil-in-water emulsion. Spontaneous emulsion flooding can be accomplished with certain crude oils containing natural emulsifiers by flooding with alkaline water. Such crude oils are usually in the lower API gravity range. Most crudes do not contain the necessary emulsifiers, however, and there is a substantial need for processes that will extend the usefulness of the spontaneous emulsion technique to include the higher API gravity oils.